Method and equipment for a treatment in molten cast iron baths with reaction materials having a low or high production of gas

ABSTRACT

This invention covers the method and equipment for the continuous or discontinuous addition of reaction/inoculation materials necessary for desulphurization or the production of ductile iron obtainable during the passage of the base iron through a basin containing the chamber for melting, vaporizing and distributing the reaction-inoculation materials into the melt (e.g. magnesium vapor-Ferrum Silicon). The treatment can be conducted continuously for unlimited or freely definable quantities of iron.

FIELD OF THE INVENTION

This invention concerns metallurgical treatments in molten bathsobtained by means of the delivery of reaction materials that can bevaporized with a high or low generation of gas and other inoculating orrefining materials.

BACKGROUND OF THE INVENTION

There already exist known metallurgical treatments in molten baths--forinstance ductile iron--which use as the reaction material puremagnesium, or its alloys, which is vaporized in the molten bath toobtain spheroidal graphite and modifications thereof, or fordesulphurization, deoxidation or similar treatments.

Using traditional techniques, vaporization is obtained by means ofdirect contact between the reaction material and the molten metal. Therequired quantity of reaction material is placed directly in the moltenmetal and heated and vaporized by it. The supply of reaction materialand the metallurgical treatment are generally discontinuous, and alsoinvolve significant loss of vapor and deformities of the bath treatment.

Known methods currently used for cast iron, particularly those usingpure metallic magnesium at atmospheric or metallostatic pressure, havean efficiency or no more than 60%; virtually 40% of the reagent fed intothe bath is lost in the form of fumes and heat. The reason for this liesin the production of vapor, which is discontinuous with irregular peaksof high pressure generated when the liquid or solid reagent comes intocontact with the molten metal.

Various methods have been designed to reduce this loss and the resultingenvironmental impact, some of which also envisage continuous treatmentof the metal flow as shown in CH-A43993599. Document CH-A-382783discloses the possibility of improving the technology by using acontinuous process of feeding the reagent material in the form of a wireinto a pressurized bell immersed in a molten bath. However, thecontinuous distribution described here does not allow constantvaporization because when the liquid/solid reagent comes into directcontact with the molten bath, it causes cooling and consequently haltsvaporization, and hence the stated aims are not attained.

More recently, a method of metallurgical treatment in a molten bath hasbeen proposed. The molten bath is of a vaporizable reaction material inwhich the reaction material is placed in at least one chamber, immersedin the molten metal and vaporized without direct contact with the metal.In effect, the reaction material is heated and vaporized through thewalls of the chamber and the vapor produced is conveyed out of thechamber towards the molten metal.

However, this method too is discontinuous although it provides someadvantages in the use and distribution of vapor in the molten metal fora more homogenous treatment.

In other words, metallurgical treatments conducted with known methodsare discontinuous considering the discontinuous supply of reactionmaterial. On the other hand, for some treatments, apart from thevaporizable material it is necessary to have inoculating or refiningmaterial for the bath. Metering and delivery to the bath of thesematerials are generally effected by simple addition during transfer ofthe metal and cause oxidation and the formation of residue leading todefects in the castings produced.

SUMMARY AND OBJECTS OF THE INVENTION

The concomitant, but separate, delivery of reaction and inoculatingmaterials effected from inside the bath in a protected atmosphere is notknown in the current state of the art. This invention aims to preventthe limitations of continuous or discontinuous metallurgical treatmentsaccording to known methods by means of a method and equipment allowingthe continuous treatment of molten material, even with a concomitantsupply of reaction materials and inoculating materials directly into thebath. This invention applies in particular to the metallurgicaltreatments of desulphurization, nodularization, etc. of iron, butwithout excluding a more general application to the treatment of otherhot liquids whether metallic or otherwise. The invention was conceived,at least as far as treatment in melt baths--particularly ductileiron--is concerned, starting from the known technique of placing thereaction material in a chamber immersed in the molten bath, but with theinnovation of feeding continuously from the external environment atatmospheric pressure, by means of a pressure-tight metering systemcontrolled by a regulator depending on the data relating to the metal totreat, materials promoting the formation of spheroids even with a highgas generation, called reagents, and separately but concomitantly, othermaterials for refining or solidifying the graphite in the bath accordingto the stable system, hereinafter referred to as inoculants.

The invention is applicable to treatments in discontinuous molten bathsin containers that can be emptied, for example, into ladles, withcontinuous delivery during the process of reagent and, if necessary,inoculant based on the metallurgical quantities and characteristicsfound, and thus known, of the bath to treat. This invention is alsoapplicable to continuous molten baths, which transit in a basin orchannel, by means of a continuous supply of reagent and, if necessary,of inoculant depending on the variable conditions of the metal arriving.

Reagents and inoculating materials are fed through a special chamber,called a reactor, the pressure of which is kept the same as themetallostatic pressure of the bath in which it is immersed and having avaporization chamber and an expansion chamber. The reagents areintroduced continuously into the vaporization chamber and pass from asolid state to a vapor by means of the high temperature of the bath or,in the case of reagents with a higher boiling point, with asupplementary supply of heat from the outside. The reagents vaporizewithout direct contact with the molten metal but with heat transmissionby conduction and radiation, before passing through the expansionchamber into a deep area of the bath and circulating therein. Theinoculants are introduced through the expansion chamber, the bottom ofwhich is formed by the bath itself, and melted by direct contact withthe molten metal, supersaturating it locally and circulating in the bathdue to the combined action of the vapors drawing the reagent materialsleaving the chamber and the metallostatic thrust exercised by the bathwhich has a greater density than the superinoculated metal.

Thus, by solubilizing they perform the chemical and physical actionsnecessary to obtain a bath with a high homogeneity, without impuritiesand ready to be poured into the molds, thereby reducing the consumptionof reagents and inoculants, energy loss and pollution.

The aims of this invention are:

to perform a discontinuous treatment, namely with definite quantities ofmetal and with known homogeneous characteristics, thus--by means of thecontinuous feeding system--reducing the quantity of reaction materialcontained in the bath and hence the development of any violent reactionsshould the solid or liquid reagents accidentally come into contact withthe bath;

to vaporize and solubilize elements with a boiling point higher than thetemperature of the bath:

to effect the addition and distribution of inoculants to favor--in castiron--solidification of the graphite according to the stable system,even simultaneously with the vaporizable element promoting the formationof spheroidal graphite and/or variants thereof;

to effect a continuous treatment, namely for indefinite quantities ofmetal with continually varying characteristics of temperature, chemicalcomposition and capacity, obtaining after the treatment a bath with therequired features;

to control continuously the process of vaporization and inoculation,regulating it to ensure the complete solubilization of thereagents/inoculants added, thus avoiding loss due to oxidation or theformation of impurities;

to eliminate difficult metallurgical operations thank to completeautomation and control of the production cycle which, in the case ofspheroidal cast iron and its variants (e.g. vermiculite), gives aninoculated material ready for casting.

Another important point is the possibility of using reagent rawmaterials with a high boiling point, such as Ca, Sr, Ba or La, whichpromote favorable metallurgical structures, and the possibility ofadapting the process in real time to the actual conditions of the metalto be processed with extremely good prospects on account of the currentstate of the art.

The various features of novelty which characterize the invention arepointed out with particularity in the claims annexed to and forming apart of this disclosure. For a better understanding of the invention,its operating advantages and specific objects attained by its uses,reference is made to the accompanying drawings and descriptive matter inwhich preferred embodiments of the invention are illustrated.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is, in vertical section, an example of equipment suitable fordiscontinuous metallurgical treatment in a molten bath in a ladle;

FIG. 2 is, in vertical section, an example of equipment suitable forcontinuous metallurgical treatment in a molten bath passing into a basinor channel;

FIG. 3 is a horizontal section according to arrows III--III in FIG. 2;

FIG. 4 is a vertical section according to arrows IV--IV in FIG. 2;

FIG. 5 is, in horizontal section, an example of multi-reactor equipmentfor continuous metallurgical treatment in a molten bath passing into abasin or channel;

FIG. 6 is a longitudinal section according to arrows VI--VI in FIG. 5;

FIG. 7 is a cross section according to arrows VII--VII in FIG. 5;

FIG. 8 is another cross section according to arrows VIII--VIII in FIG.5; and

FIG. 9 is a cross section of a further configuration of the reactor formetallurgical treatment according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The method of treatment according to the invention includes continuousdelivery of a reagent 10 and, if necessary, inoculant 11 into acontinuous or discontinuous molten bath, namely a known or indefinitequantity. The bath, if of a known and definite quantity, may becontained in a vessel such as a ladle 13 and changed after eachtreatment; if of an indefinite quantity, it may flow through a vesselsuch as a basin or along a channel 14.

Such delivery of the reagent 10 or inoculant 11 is obtained by means ofat least one special container unit 15 immersed in the molten bath to betreated 12, hereinafter referred to as a reactor and having avaporization chamber 16 and an expansion chamber 17, interconnecting bymeans of a passage 18 situated at a set level above the vaporizationchamber 16 and/or the free surface. Each reactor may be in a singlepiece or comprised of various parts, even not homogenous, but made of agas-tight material with appropriate physical and mechanical propertiesto withstand operating stress and maintain the internal pressure whichis generated inside during the reactions and which prevents the moltenmetal from returning into the expansion chamber. It should be noted thatthe reactor can be installed in a fixed or movable position.

The vaporization chamber 16 and the expansion chamber 17 may be coaxialor placed side by side. Correspondingly, the geometry of the reactor 15may vary widely from execution, as may the configuration of the reactorin or in relation to the bath to treat. Correspondingly, the reactor 15may be in the shape of an immersed bell in the center or to one side ofthe molten bath in a ladle 13, as shown in FIG. 1. Alternatively, thereactor 15 may be in the shape of a block placed along the wall of atank or channel 14 as shown in FIGS. 5-8. In all cases, the vaporizationchamber 16 is open at the top and communicates only with the expansionchamber 17 through the passage 18, and not with the bath. The moltenbath is only in contact with the side walls and/or bottom of thevaporization chamber 16. On the other hand, the expansion chamber 17communicates at the top with the vaporization chamber 16 through thepassage 18, whereas at the bottom and/or side it is completely orpartially open directly towards the molten bath through possiblepassages 17'.

To the vaporization chamber 16 there is connected a first duct 19 fordelivering the reagent material contained in and coming from a firstsupply tank/metering unit 20, 20' (in the drawings this tank/meteringunit is represented for granular materials, but it may be envisaged formaterials in wire or powder form.) To the expansion chamber there isconnected a second duct 21 for delivering inoculating material 11contained in and coming from a second tank/metering unit 22, 22'. Thetanks/metering units 20, 22 are situated superiorly over or anyway outof the molten treatment bath 12 and the ducts 19, 21 from thetanks/metering units may be united in a single assembly or separate fromeach other. In any case, the reagent 10 and the inoculant 11 aredelivered separately, although concomitantly, into the vaporizationchamber 16 and the expansion chamber 17, respectively.

For treatment in a molten bath 12 in a ladle 13, the latter and theequipment for supplying the reagent and inoculant are suitably pressuresealed and fitted with efficient control and safety systems.

In practice, the molten bath 12, whether it be in a ladle 13 or passinginto a basin or channel 14, when coming into contact with the reactor 15transfers the fusion/vaporization heat to the reagent 10 contained inthe chamber 16. The vapor produced passes through the passage 18 placedin a higher position than the level of the bath in the expansion chamber17 and from this it is blown into the bath 12 through the passages 17'in the bottom of the chamber. The vapor rises towards the surfacesolubilizIng and distributing itself for the desired reactions. Themetal can not rise back up into the expansion chamber 16 in that thepressure in the same is in constant equilibrium with the metallostaticpressure.

The delivery of reagent material 10 into the vaporization chamber 16 isactuated by means of the metering system 20, 20' controlled by aregulator and contained in a hopper that can be pressurized with inertgas equipped with a stop valve 20" (FIG. 7) which, as the reagent passesfrom the hopper 20 at atmospheric pressure into the relevant duct 19,prevents the vapor from escaping. The metering unit 20' is hermeticallysealed and ensures maintenance of the pressure inside the hopper 20during metering and acts as a base for the hopper holding a definitequantity of reagent. The opening of the metering unit 20' is controlledby a minimum level gauge 23 to ensure the constant presence of reagent.Depending on the quantity of reagent introduced into the chamber 16 viathe distribution duct 19, the level of reagent varies and parallel thedegree of vaporization and the quantity of reagent passing into the bathin the unit of time.

The tank/metering unit 22, 22', which is designed for feedinginoculating materials 12 into the expansion chamber 17 through thedistribution duct, operates in the same way. The metal treated andpossibly inoculated is tapped by a spout 24 (FIG. 6) where as the slag25 produced collects on the wall of the basin from which it can easilybe removed manually or automatically. Upon completion of the treatment,the basin is emptied through a discharge outlet 26 which allows gradualtapping of the metal and the simultaneous reduction of pressure toatmospheric level in the chambers 16, 17 of the reactor 15.

The system designed for continuous operation is equipped with thenecessary control and safety systems represented by a probe 27 (FIGS. 2and 9) for controlling the level of the reagent 10 which regulatesclosing of the valve; a system 28 (FIG. 6) for continuous measurement ofthe pressure inside the reactor which shuts off the valve when setvalues are exceeded; a safety valve 29 with instant opening; a basincover 30; a siphoning system 31 (FIG. 6)--shown in the rest position; aprotection bulkhead 32 which circumscribes the system; and a gas suctionand removal system (not represented). Lastly each reactor 15 may beequipped with a unit 33 operated by electricity, gas, etc. for heatingthe reagent 10 in the vaporization chamber when the reagent has avaporization point exceeding the temperature of the melt.

While specific embodiments of the invention have been shown anddescribed in detail to illustrate the application of the principles ofthe invention, it will be understood that the invention may be embodiedotherwise without departing from such principles.

I claim:
 1. A method for metallurgical treatment of a molten bath, themethod comprising the steps of:providing a molten bath; providing areactor in the molten bath; adding reagent material to said reactorwhile said reactor is in the molten bath; vaporizing said reagentmaterial in said reactor while said reagent material is spaced fromliquid of the molten bath; mixing vapor from said reagent material withthe molten bath.
 2. The method in accordance with claim 1, wherein:themolten bath is a metal molten bath.
 3. The method in accordance withclaim 1, wherein:said adding of reagent material is continuous.
 4. Themethod in accordance with claim 1, wherein:said vaporizing of saidreagent material is performed without direct contact with the moltenbath.
 5. The method in accordance with claim 1, furthercomprising:adding inoculating material to said reactor.
 6. The method inaccordance with claim 5, further comprising:vaporizing said inoculatingmaterial in said reactor while said inoculating material is spaced fromliquid of the molten bath; mixing vapor from said inoculating materialwith the molten bath.
 7. The method in accordance with claim 6,wherein:said inoculating material is continuously fed spaced from, andconcurrently with, said reagent material.
 8. The method in accordancewith claim 1, wherein:said vaporizing is performed with heat additionalto heat from the molten bath.
 9. The method in accordance with claim 1,wherein:said vaporizing is performed while said reagent material isspaced from liquid in liquid contact with the molten bath; said addingis substantially simultaneous with said mixing.
 10. The method inaccordance with claim 1, wherein:said reagent material has no liquidcontact with the molten bath.
 11. A device for metallurgically treatinga molten bath, the device comprising:a reactor positionable in themolten bath, said reactor defining a reagent vaporization chamber forreceiving and vaporizing reagent material, said reactor defining aninoculant vaporization chamber for receiving and vaporizing inoculatingmaterial, said reactor defining a passage communicating said reagent andinoculant vaporization chambers; first metering unit for metering anddelivering continuously the reagent material to said reagentvaporization chamber; second metering unit for separately metering anddelivering continuously the inoculating material to said inoculantvaporization chamber.
 12. The device in accordance with claim 11,wherein:said reagent vaporization chamber has walls in contact with themolten bath; said inoculant vaporization chamber has an opening incommunication with the molten bath, said reagent and inoculantvaporization chambers have means for pressurizing said chambers andpreventing the molten bath from entering said inoculant vaporizationchamber.
 13. The device in accordance with claim 11, wherein:saidreagent and inoculant vaporization chambers are united concentrically ina body with respect to one another.
 14. The device in accordance withclaim 11, wherein:said reagent and inoculant vaporization chambers arearranged one beside the other in a body.
 15. The device in accordancewith claim 11, further comprising:a heating unit in said reagentvaporization chamber for heating the reagent material.
 16. The device inaccordance with claim 11, further comprising:duct work for guiding thereagent material and inoculating material from said first and secondmetering units.
 17. The device in accordance with claim 11, wherein:saidreactor is immersed in the molten bath.
 18. The device in accordancewith claim 11, wherein:one of a tank and a channel holds the moltenbath; said reactor is arranged on a wall of said one of said tank andchannel.
 19. The device in accordance with claim 11, wherein:saidreagent vaporization chamber holds the reagent material spaced fromliquid of the molten bath.